1. Field of the Invention
The present invention relates to a method and apparatus for treating a disc plate. More specifically, the present invention relates to the method and the apparatus for reducing a warp of an optical disc such as a digital video disc (hereinafter referred to as xe2x80x9cDVDxe2x80x9d) and a compact disc. Especially, the warp is the one that is caused to a disc plate (of the optical disc) which has been molded through an injection molding. With the thus reduced warp, the disc plate is flattened.
2. Description of the Related Art
Generally, an optical disc plate such as a DVD plate and a compact disc plate is molded through an injection molding.
As is seen in FIG. 14(A), FIG. 14(B) and FIG. 14(C), there is provided a method of molding a disc plate 1. A resin material is injected into a pair of a first metal mold 10 and a second metal mold 11 for an injection molding. After the injection molding, the resin material is molded into a mold disc plate 1xe2x80x2 which is to be solidified to become the disc plate 1. At this point in time, a predetermined information is recorded on one of two surfaces of the mold disc plate 1xe2x80x2. After this, as is seen in FIG. 14(B), the first metal mold 10 and the second metal mold 11 are separated from each other (opened). Then, a takeout arm 12 of a takeout mechanism (not shown) moves forward into an area between the first metal mold 10 and the second metal mold 11, to thereby securely absorb the mold disc plate 1xe2x80x2 which is high in temperature and is still soft. After this, the takeout arm 12 moves backward, to thereby take the mold disc plate 1xe2x80x2 out of the first metal mold 10 and the second metal mold 11.
Then, as is seen in FIG. 14(C), in a predetermined position, the thus taken out mold disc plate 1xe2x80x2 is fixedly absorbed directly with a conveyer arm 13 of a conveyance mechanism. The conveyer arm 13 conveys the mold disc plate 1xe2x80x2 to a cooling stage 14 (next operation).
More specifically, the mold disc plate 1xe2x80x2 has a first surface and a second surface opposite to the first surface. On the first surface, the mold disc plate 1xe2x80x2 is fixedly absorbed to a tip end 12A of the takeout arm 12. On the second surface, the mold disc plate 1xe2x80x2 is fixedly absorbed to a tip end 13A of the conveyer arm 13. Simultaneously with the absorption of the mold disc plate 1xe2x80x2 to the tip end 13A, the tip end 12A releases (namely, stops absorbing) the mold disc plate 1xe2x80x2. Then, the conveyer arm 13 turns by substantially 180xc2x0 with the mold disc plate 1xe2x80x2 fixedly absorbed to the tip end 13A. Thereafter, the conveyer arm 13 conveys the mold disc plate 1xe2x80x2 to the cooling stage 14. The mold disc plate 1xe2x80x2 is cooled with the cooling stage 14, to thereby solidify the resin material of the mold disc plate 1xe2x80x2. After the solidification, the mold disc plate 1xe2x80x2 is referred to as the disc plate 1. The solidification temperature for solidifying the resin material is, for instance, about 90xc2x0 C.
As described above, the mold disc plate 1xe2x80x2 soon after being taken out of the first metal mold 10 and the second metal mold 11 is high in temperature, and is sufficiently soft. Therefore, during the sequential operations of i) cooling, ii) solidification of resin material, and iii) becoming the disc plate 1, the mold disc plate 1xe2x80x2 causes a considerable deformation such as warp. Conventionally, various methods are taken so as to reduce the warp by adjusting conditions of the injection mold as below:
i) Adjust temperature of the first metal mold 10 and the second metal mold 11 of a mold machine.
ii) Set up temperature difference between the first metal mold 10 and the second metal mold 11.
iii) Adjust pressure for injecting the resin material.
Even if the warp of the mold disc plate 1xe2x80x2 is small and reduced through the conventional methods as described above, the mold disc plate 1xe2x80x2 causes the warp during the time the mold disc plate 1xe2x80x2 is taken out of the first metal mold 10 and the second metal mold 11, and during the time the mold disc plate 1xe2x80x2 is conveyed to the cooling stage 14. The thus caused warp is attributable to the following repeated description, that is, xe2x80x9cThe mold disc plate 1xe2x80x2 soon after being taken out of the first metal mold 10 and the second metal mold 11 of the mold machine is high in temperature and is sufficiently soft.xe2x80x9d Moreover, the thus caused warp grows during the cooling operation.
The warp is more specifically described in FIG. 15(A), FIG. 15(B) and FIG. 15(C). The mold disc plate 1xe2x80x2 is taken out of the first metal mold 10 and the second metal mold 11 of the mold machine. As is seen in FIG. 15(A), the mold disc plate 1xe2x80x2 is fixedly absorbed to the tip end 12A of the takeout arm 12. Moreover (otherwise), the mold disc plate 1xe2x80x2 is fixedly absorbed to the tip end 13A of the conveyer arm 13. The mold disc plate 1xe2x80x2 is high in temperature and is sufficiently soft. Therefore, the mold disc plate 1xe2x80x2 causes the warp when the mold disc plate 1xe2x80x2 is absorbed substantially in the center area of the mold disc plate 1xe2x80x2, in such a manner that the warp is bent opposite {(rightward in FIG. 15(A)} to an absorption side. Especially, the DVD having a thickness of about 0.6 mm (thin) shows the warp (bend) more outstanding than the compact disc having a thickness of about 1.2 mm. Moreover, as is seen in FIG. 15(B), the mold disc plate 1xe2x80x2 is turned by the takeout arm 12 at a comparatively high speed with the mold disc plate 1xe2x80x2 absorbed by the takeout arm 12, and the mold disc plate 1xe2x80x2 is conveyed by the conveyer arm 13 at a comparatively high speed with the mold disc plate 1xe2x80x2 absorbed by the conveyer arm 13. The above turn and conveyance of the mold disc plate 1xe2x80x2 causes a wind pressure, to thereby warp the mold disc plate 1xe2x80x2. Moreover, as is seen in FIG. 15(C), the mold disc plate 1xe2x80x2 is cooled on a disc bench 15 of the cooling stage 14. The mold disc plate 1xe2x80x2 has such a dead weight as to, as the case may be, cause the warp during a cooling time on the disc bench 15. Still furthermore, some other cooling stages having different constitution cause a partial deformation of the mold disc plate 1xe2x80x2 during the cooling time.
The above warp is caused around a center hole (not shown) of the mold disc plate 1xe2x80x2 radially outward, to thereby form substantially a point symmetry. Some other warps run in such a manner as to form a bilateral symmetry (rightward and leftward) with respect to one to three line(s) through the center hole. The above warps become more obvious as production cycle time of the disc plate 1 is shortened, to thereby encourage the warp (more complicated and larger) of the disc plate 1.
It is an object of the present invention to provide a method and an apparatus for treating a disc plate.
More specifically, it is the object of the present invention to obtain the disc plate having a warp or a deformation within an allowable limit (tolerance), or to obtain the disc plate which is substantially free from the warp or the deformation. For obtaining the above disc plate, a mold disc plate is spun, during the time the resin material of the mold disc plate is soft (in other words, before solidification of the resin material), at such a high speed as to cause a centrifugal force. Simultaneously with this, the mold disc plate is cooled down. The centrifugal force helps reduce the warp and the deformation.
According to a first aspect of the present invention, there is provided a method of treating a disc plate. The method comprises the following operations of: molding a mold disc plate through an injection molding; and spinning the mold disc plate at a high spin speed. The spinning operation comprises at least one of the following two sub-operations of: reducing a warp of the mold disc plate with a centrifugal force caused during the spinning operation, and reducing a temperature of the mold disc plate during the spinning operation.
According to a second aspect of the present invention, there is provided an apparatus of treating a disc plate. The apparatus comprises: a conveyer for conveying a mold disc plate obtained through an injection molding; a disc bench for receiving the mold disc plate conveyed with the conveyer; and a spin driver for spinning the disc bench when a temperature of the mold disc plate is higher than 90xc2x0 C., to thereby spin the mold disc plate.
The other objects and features of the present invention will become understood from the following description with reference to the accompanying drawings.